Recently, portable terminals such as cellular phones and portable information devices have been rapidly developed to offer multiple functions. Along with this trend, there has emerged a demand to connect these portable terminals with other equipment. There has also emerged a problem of increased power consumption due to prolonged hours of usage. In order to solve such demand and problem, it is desired to increase the capacity of batteries for the portable terminals. On the other hand, by the nature of the portable terminals, there is still a strong demand to reduce the weight and size to improve the portability thereof.
In order to meet these contradictory demands, it is for example proposed to assign functions of some parts pertaining to a base unit (for example, functions of a connector for data communication) to a cradle device, which is originally used as a stationary holder for charging the base unit.
As the number of functions that the cradle device takes charge of is increased, it becomes necessary for a user to carry the cradle device as well. For example, Japanese Laid-Open Patent Publication No. 2001-101140 (Patent Document 1) and No. 2003-110677 (Patent Document 2) disclose a cradle which is formed foldable to give it portability. On the other hand, Japanese Patent No. 2711784 (Patent Document 3) focuses on improving the portability of a battery pack charger.
However, these cradle devices have several problems.
The first problem resides in the fact that these prior art examples put focus on the portability of the cradle by itself, and no consideration is given to the portability when the cradle device is connected to a portable terminal. When the cradle device has additional functions that the portable terminal does not have, it is necessary to improve the portability of the cradle device connected to the portable terminal.
The second problem resides in the fact these conventional cradle devices have low mechanical reliability. Although consideration is given to connectability to the base unit, no consideration is given to high mechanical reliability that the cradle device should have when carried in the condition connected to the portable terminal represented by a cellular phone.